Peter A.B. Orlean
Professor of Microbiology
Burroughs Wellcome Scholar in Molecular Pathogenic Mycology
p-orlean@uiuc.edu
B.Sc. (Bacteriology), University of Newcastle-upon-Tyne, 1977
M.Phil. (Biochemistry), University of Cambridge, 1978
Ph.D. (Biochemistry), University of Cambridge, 1982
Post-Doctoral (Cell Biology), Universität Regensburg, 1983-1985
Post-Doctoral (Molecular Biology), Massachusetts Institute of Technology, 1985-1990
Synthesis and function of glycosylphosphatidylinositol membrane anchors; molecular genetics of cell wall biogenesis in yeast and pathogenic fungi.
Fungal cell walls are dynamic three-dimensional complexes of polysaccharides and glycoproteins that confer cell integrity and dictate cell shape, yet which also permit cell expansion and cell division. Because the wall is essential for cell viability and because surface glycoproteins are important virulence determinants in fungal pathogens, inhibition of cell wall biogenesis should be an excellent strategy for combating fungal infections. We are charting the biosynthetic pathways for the assembly of yeast cell wall components and pinpointing steps that have no essential counterpart in mammals and which could therefore be targeted by new antifungal drugs.
We are focusing on glycosylphosphatidylinositols (GPIs). These have a core structure of protein-CO-NH-CH2-CH2-PO4-6-mannose-a1, 2-mannose-a1, 6-mannose-a1, 4-glucosamine-a1, 6-inositol-phospholipid, which can be decorated with phosphoethanolamine and mannose side-branches. This glycolipid is built up stepwise by enzymes in the membrane of the rough endoplasmic reticulum, then attached to the COOH terminus of certain secretory glycoproteins. GPI-modified proteins are then transported to the cell surface where they may remain anchored in the external face of the plasma membrane or become cross-linked to the yeast cell wall upon formation of a covalent link between the GPI glycan and cell wall b-glucan.
We are using genetics, bioinformatics, molecular biology, and biochemistry to study how GPIs are made in Saccharomyces cerevisiae. Our strategy is to isolate single and double gpi mutants and to determine where they are blocked in GPI synthesis by analyzing the structures of the GPI assembly intermediates that accumulate when the mutational block is imposed. This approach is allowing us to order the steps in GPI assembly, to clone the genes involved, and to carry out structure-function studies of the enzymes these GPI synthesis genes encode. Our work with gpi mutants has established that GPIs are essential for viability and for normal cell wall morphogenesis.
We are using the know-how we have gained from our studies of S. cerevisiae to explore GPI assembly in the pathogenic fungus Candida albicans. We have established that GPIs are essential in this organism, and have shown that the CaSMP3 gene encodes an essential GPI mannosyltransferase whose activity appears to be absent from or dispensible in mammals. This enzyme represents a new potential target for antifungal drugs, agents that are sorely needed to combat the Candida infections that afflict immunocompromised patients.
Fabre, A.-L., Orlean, P., and Taron, C.H. (2005) "Saccharomyces cerevisiae Ybr004c and its human homologue are required for addition of the second mannose during glycosylphosphatidylinositol precursor assembly," The FEBS Journal, in press.
Grimme, S.J., Colussi, P.A., Taron, C.H., and Orlean, P. (2004) "Deficiencies in the essential Smp3 mannosyltransferase block glycosylphosphatidylinositol assembly and lead to defects in growth and cell wall biogenesis in Candida albicans," Microbiology 150: 3115-3128. [Abstract]
Sobering, A.K., Watanabe, R., Romeo, M.J., Yan, B.C., Specht, C.A., Orlean, P., Riezman, H., and Levin, D.E. (2004) "Yeast Ras regulates the complex that catalyzes the first step in GPI-anchor biosynthesis at the ER," Cell 117: 637-648. [Abstract]
Grimme, S.J., Gao, X.-D., Martin, P.S., Tu, K., Tcheperegine, S.E., Corrado, K., Farewell, A.E., Orlean, P., and Bi, E. (2004) "Deficiencies in the endoplasmic reticulum (ER)-membrane protein Gab1p perturb transfer of glycosylphosphatidylinositol to proteinsand cause perinuclear ER-associated actin bar formation," Mol. Biol. Cell 15: 2758-2770. [Abstract]
Kostova, Z., Yan, B.C., Vainauskas, S., Schwartz, R., Menon, A.K., and Orlean, P. (2003) "Comparative importance in vivo of conserved glutamates in the EX7E-motif retaining glycosyltransferase Gpi3p, the UDP-GlcNAc-binding subunit of the first enzyme in glycosylphosphatidylinositol assembly," Eur. J. Biochem. 270: 4507-4514. [Abstract]
View Publications by Peter A.B. Orlean listed on the National Library of Medicine (PubMed)